Topic 6

• 6.1.1 Explain why digestion of large food molecules is essential

  ◾Most food molecules are large polymers and insoluble

  ◾They must first be digested to smaller soluble molecules before they can be absorbed into the blood
• 6.1.2 Explain the need for enzymes in digestion

  ◾Enzymes are biological catalysts that increase the rate of reaction

  ◾Digestive enzymes are secreted into the lumen of the gut

  ◾Digestive enzyme increase the rate of reaction of the hydrolysis of insoluble food molecules to soluble end products

  ◾Digestive enzymes increase the rate of reaction at body temperature
• 6.1.3 State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase

  
• 6.1.5 Outline the function of the stomach, small intestine and large intestine

  Stomach

  ◾ Protein digestion begins and bacteria are killed by HCl

  ◾The stomach contains gastric glands which secrete digestive juices for chemical digestion- pepsinogen is changed to pepsin (protease) by HCl and begins chemical digestion

  ◾Acids create a low pH environment (pH~1-2) that begins to denature proteins, while proteases like pepsin hydrolyse large proteins

  ◾The stomach also releases a hormone (gastrin) that regulates stomach secretions

  ◾The mechanical action of the stomach (churning) also promotes digestion by mixing the food

  Small Intestine

  ◾The small intestine is where usuable food substances (e.g. nutrients) are absorbed into the bloodstream by diffusion, active transport and facilitated diffusion

  ◾The pancreas and gall bladder (via the bile duct) both secrete substances into the small intestine to aid in digestion

  ◾The small intestine is lined with smooth muscle to allow for the mixing and moving of digested food products (via segmentation and peristalsis) ◾It also contains small pits (crypts of lieberkuhn) that secrete intestinal juices

  ◾The small intestine contain infoldings called villi, to increase surface area and optimise the rate of absorption. Microvilli on villi to further increase SA:Vol.

  Large Intestine

  ◾The large intestine absorbs water and dissolved minerals (also helps make Vitamin K) from the indigestible food residues, and by doing so converts what remains from a fluid state into a semi-solid faeces

  ◾The faeces is stored in the rectum and eliminated out the anus
• 6.1.6 Distinguish between absorption and assimilation

  Absorption: The movement of a fluid or dissolved substances across a membrane

  Assimilation: The conversion of nutrients into fluid or solid parts of an organism in cells (when tissues take them up and use them)

  Hint: Absorption is taking it into something, assimilation is making it a part of something
• 6.1.7 Explain how the structure of the villus is related to its role in absorption and transport of products of digestion

  Learn the mnemonic - MRSLIM for villus features and functions:

  Microvilli: Greatly increase the surface area of the villus, allowing for a greater rate of absorption

  Rich capillary networks: Help to maintain a concentration gradient for absorption by rapidly transporting absorbed products away

  Single epithelial layer: Ensures minimal diffusion distance between the intestinal lumen and capillary network

  Lacteals: Absorb lipids from the intestine into the lymphatic system (which are later reabsorbed back into normal circulation)

  Intestinal crypts: Located between villi and release juices that act as a carrier fluid for nutrients

  Membrane proteins / mitochondria: High amounts to enable active transport into cells (contents then passively diffuse into bloodstream)

  
• 6.2.2 State that coronary arteries supply heart muscle with oxygen and nutrients

  ◾The heart is a muscle that must continually contract in order to pump blood around the body

  ◾Coronary arteries form a network of vessels around the heart and supply the cardiac tissue with oxygen and nutrients (i.e. glucose)

  ◾These are required to produce the necessary energy via aerobic respiration - if a coronary artery is blocked, a heart attack may occur
• 6.2.3 Explain the action of the heart in terms of collecting blood, pumping blood and opening and closing valves

  atria collect blood from veins (vena cava/pulmonary);

  collect blood while ventricles are contracting;

  atria pump blood into ventricles;

  ventricles pump blood into arteries and out of the heart;

  ventricles pump blood at high pressure because of their thicker,

  muscular walls;

  left ventricle pumps blood out to the body (aorta) and and right ventricle pumps blood to lungs (pulmonary artery);

  The heart valves maintain the one-way flow of blood;

  When the atria contract, atrioventricular (AV) valves open;

  Blood flows from the atria and into the ventricles;

  When the ventricles contract, the AV valves close and semi-lunar valves open;

  This forces blood out of the ventricles and into the arteries;

  As arterial pressure drops, the semi-lunar valves close, ensuring the one-way flow of blood;
• 6.2.4 Outline the control of the heartbeat in terms of myogenic muscle contraction, the role of the pacemaker, nerves, the medulla of the brain and epinephrine (adrenaline)


  the heart is myogenic / beats on its own accord;

  60-80 times a minute (at rest);

  coordination of heartbeat is under the control of pacemaker;

  located in the muscle / walls;

  sends out signal for contraction of heart muscle;

  atria contract followed by ventricular contraction;

  fibres / electrical impulses cause chambers to contract;

  nerve from brain can cause heart rate to speed up;

  nerve from brain can cause heart rate to slow down;

  adrenalin/epinephrine (carried by blood) speeds up heart rate;

  artificial pacemakers can control the heartbeat;

  ;Sympathetic nerves speed up heart rate ;Parasympathetic nerves slow down heart rate
• 6.2.5 Explain the relationship between the structure and function of arteries, capillaries and veins

  arteries carry blood leaving heart;

  so have thick walls to withstand high pressure;

  arteries have muscles to allow elasticity / recoiling;

  arteries have narrow lumen to maintain high pressure;

  capillaries are site of materials exchange;

  capillaries have a single layer of cells so diffusion distance is short;

  capillaries have narrow lumen / width of single blood cell;

  to fit into small places / provide large surface area:volume ratio for gas exchange;

  veins return blood to the heart;

  veins have thinner walls / large lumen (to reduce resistance to flow);

  (allows them to be) pressed by adjacent muscles to move blood;

  veins do not support high pressure (as they carry blood to heart);

  veins have valves to avoid backflow;See an expert-written answer!We have an expert-written solution to this problem!
• 6.2.6 State that blood is composed of plasma, erythrocytes, leukocytes (phagocytes and lymphocytes) and platelets

  There are four main components to blood:

  ◾Plasma - the fluid medium of the blood

  ◾Erythrocytes - red blood cells (involved in oxygen transport)

  ◾Leukocytes - white blood cells, such as phagocytes (non-specific immunity) and lymphocytes (specific immunity)

  ◾Platelets - responsible for blood clotting (haemostasis)
• 6.2.7 State that the following are transported by blood: nutrients, oxygen, carbon dioxide, hormones, antibodies, urea and heat

  ◾Nutrients (e.g. glucose)

  ◾Antibodies

  ◾Carbon dioxide

  ◾Hormones

  ◾Oxygen

  ◾Urea

  ◾Heat (not a molecules, unlike all the others)
• 6.3.1 Define pathogen


  A pathogen is a disease-causing micro-organism, virus or prion
• 6.3.2 Explain why antibiotics are effective against bacteria but not against viruses

  ◾Antibiotics are substances or compounds that kill or inhibit the growth of bacteria by targeting the metabolic pathways of prokaryotes

  ◾Specific prokaryotic features that may be targeted by antibiotics include key enzymes, 70S ribosomes and the bacterial cell wall

  ◾Because eukaryotic cells do not have these features, antibiotic can kill bacterial cells without harming humans (or viruses)

  ◾Virus do not carry out metabolic reactions themselves but instead infect host cells and take over their cellular machinery

  ◾Viruses need to be treated with specific antiviral agents that target features specific to viruses (e.g. reverse transcriptase in retroviruses)
• 6.3.3 Outline the role of skin and mucous membranes in defence against pathogens

  Skin:

  lower pH / acid to keep bacteria from growing / chemical barrier;

  fatty acids / waxes antimicrobial;

  physical barrier to prevent entry / dry skin inhibits bacterial growths;

  bacteria on skin / mucous membranes prevent other bacteria from growing;

  antimicrobial / lysozyme in sweat and saliva (mucous membrane) to keep bacterial growth in check;

  mucous membranes:

  mucous traps bacteria / sticky / mucus slightly acidic ie vagina;

  cilia sweep mucous up to be swallowed to kill bacteria;

  contain macrophages / phagocytes;
• 6.3.4 Outline how phagocytic leucocytes ingest pathogens in the blood and in body tissue

  phagocytic leucocyte occurs in blood and body tissue fluids;

  phagocytic leucocyte detects pathogen/foreign material;

  leucocyte surrounds/engulfs pathogen / endocytosis / phagocytosis;

  membrane forms around pathogen to form a vacuole;

  lysosomes digest contents of vacuoles;
• 6.3.5 Distinguish between antigens and antibodies

  Antigen: A substance that the body recognises as foreign and that can evoke an immune response

  
  

  Antibody: A protein produced by certain white blood cells (B lymphocytes, plasma cells) in response to an antigen
• 6.3.6 Explain antibody production

  antigens stimulate an immune response;

  antibodies are produced in response to specific antigens;

  antibodies are made by B-cells / lymphocytes / plasma cells;

  antigen is engulfed by macrophages;

  antigen is presented on macrophage membrane;

  helper T-cells bind to antigen (on macrophage);

  helper T-cells are activated;

  helper T-cells activate B-cells;

  B-cells clone;

  into plasma cells and memory cells;

  plasma cells produce specific antibodies to the antigen;

  memory cells for long-term immunity;

  a faster / stronger response later;
• 6.3.7 Outline the effect of HIV on the immune system

  HIV/human immunodeficiency virus;

  reduces the effectiveness of the immune system / reduction in

  the number of active lymphocytes / infects T-(helper) cells/

  lymphocytes;

  loss of the ability to produce antibodies;

  leaving the infected person susceptible to other infectious

  diseases / AIDS is an accumulation of opportunistic diseases;
• 6.3.8 Discuss the cause, transmission and social implications of AIDS

  cause:

  human immunodeficiency virus / HIV / HIV 1 and HIV 2;

  retrovirus / RNA to DNA;

  enters T-helper cells;

  immune system becomes disabled / weakened;

  greater chance for opportunistic infections;

  transmission:

  sexually transmitted;

  can be transmitted from man to woman;

  saliva and other body fluids;

  use of dirty needles;

  blood transfusions;

  social implications of AIDS:

  many orphaned children;

  social stigma / discrimination;

  problems obtaining employment / life insurance;

  costs on health systems of treating people;

  early death reduces family income;

  drug treatment expensive;

  encourages use of condoms;
• 6.4.1 Distinguish between ventilation, gas exchange and cell respiration

  Respiration is the transport of oxygen to cells where energy production takes place, and involves three key processes:

  ◾Ventilation: The exchange of air between the lungs and the atmosphere; it is achieved by the physical act of breathing

  ◾Gas exchange: The exchange of oxygen and carbon dioxide in the alveoli and the bloodstream; it occurs passively via diffusion

  ◾Cell Respiration: The release of ATP from organic molecules; it is greatly enhanced by the presence of oxygen (aerobic respiration)
• 6.4.2 Explain the need for a ventilation system

  draws fresh air / oxygen into the lungs;

  oxygen used for respiration in all cells;

  removal / excretion of CO2 waste product from respiration;

  maintains concentration gradient of O2 / CO2 / respiratory gases;

  enables efficient gas exchange
• 6.4.3 Describe the features of alveoli that adapt them to gas exchange

  large surface area (to lung) for faster diffusion rate;

  single cell wall / layer; gives small distance for gases (Oxygen and CO2) to travel;

  moist lining; allows gases to dissolve and diffuse across into blood/out of alveoli more rapidly;

  dense network of capillaries; to maintain concentration gradient in blood;
• 6.4.5 Explain the mechanism of ventilation of the lungs in terms of volume and pressure changes caused by the internal and external intercostal muscles, the diaphragm and abdominal muscles

  inhalation:

  diaphragm contracts;

  (external) intercostal muscles contract;

  internal intercostal muscles relax;

  increased volume (of thorax / thoracic cavity);

  decreasing air pressure in lungs;

  air rushes in down air pressure gradient;

  converse of the above causes exhalation;

  abdominal muscles contract during active exhalation;

  elastic recoil of lungs helps exhalation;
• 6.5.1 State that the nervous system consists of the central nervous system (CNS) and peripheral nerves, and is composed of cells called neurons that carry rapid electrical impulses


  Neurons are cells that are specialised for the conduction of nerve impulses and serve as the fundamental unit of the nervous system

  The nervous system can be divided into two main parts:

  ◾Central Nervous System (CNS): Made up of the brain and the spinal cord

  ◾Peripheral Nervous System (PNS): Made of peripheral nerves which link the CNS with the body's receptors and effectors
• 6.5.3 State that nerve impulses are conducted from receptors to the CNS by sensory neurons, within the CNS by relay neurons, and from the CNS to effectors by motor neurons

  There are three main types of neurons in the nervous system:

  ◾Sensory Neurons: Conduct nerve impulses from receptors to the CNS (afferent pathway)

  ◾Relay Neurons: Conduct nerve impulses within the CNS (also called interneurons or connector neurons)

  ◾Motor Neurons: Conduct nerve impulses from the CNS to effectors (efferent pathway)
• 6.5.4 Define resting potential and action potential (depolarisation and repolarisation)

  Resting Potential: The charge difference across the membrane when a neuron is not firing (-70 mV), as maintained by the sodium-potassium pump

  Action Potential: The charge difference across the membrane when a neuron is firing (about 30 mV)

  Depolarisation: The change from a negative resting potential to a positive action potential (caused by opening of sodium channels)

  Repolarisation: The change from a positive action potential back to a negative resting potential (caused by opening of potassium channels)
• 6.5.5 Explain how a nerve impulse passes along a non-myelinated neuron

  resting membrane is polarized;

  interior is -70 mV/negative relative to outside;

  more sodium ions outside than inside;

  more potassium ions inside than outside;

  disturbance of membrane opens sodium ion channels;

  sodium ions rush to inside of cell;

  causing depolarization;

  sodium ion channels shut;

  potassium ion channels open;

  potassium ions rush out;

  helping to restore polarized state of membrane;

  sodium-potassium pumps maintain polarity;

  process repeated along the length of neuron / sodium ions diffuse between region with an action potential and the region at resting potential;
• 6.5.6 Explain the principles of synaptic transmission


  nerve impulse travels to end of presynaptic neuron;

  triggers influx of Ca2+;

  causes synaptic vesicles to fuse with membrane;

  release neurotransmitter molecules into synaptic cleft;

  (neurotransmitter) crosses / diffuses across channel;

  (neurotransmitter) binds to receptors on next / postsynaptic neuron;

  causes ion channels to open on neuron;

  eg Na+ diffuse into postsynaptic neuron;

  can inhibit / excite;

  by hyperpolarizing / depolarizing;

  neurotransmitter degraded;

  Ca2+ pumped back into the synaptic cleft;

  acetylcholine is a neurotransmitter;
• 6.5.7 State that the endocrine system consists of glands that release hormones that are transported in the blood


  An endocrine gland is a ductless gland in the body that manufactures chemical messengers called hormones and secretes them directly into the blood

  
  

  Hormones act on distant sites (target cells) and tend to control slow, long-term activities such as growth and sexual development
• 6.5.8 State that homeostasis involves maintaining the internal environment between limits, including blood pH, carbon dioxide concentration, blood glucose concentration, body temperature and water balance

  Homeostasis is the tendency of an organism or cell to maintain a constant internal environment within tolerance limits

  Internal equilibrium is maintained by adjusting physiological processes, including:

  ◾Body temperature (normally 36 - 38°C)

  ◾Blood pH (normally 7.35 - 7.45)

  ◾Carbon dioxide concentration (normally 35 - 45 mmHg)

  ◾Blood glucose concentration (normally 75 - 95 mg / dL)

  ◾Water balance (varies with individual body size)
• 6.5.9 Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms

  ◾Most homeostatic control mechanisms operate through a negative feedback loop

  ◾When specialised receptors detect a change in an internal condition, the response generated will be the opposite of the change that occurred

  ◾When levels have returned to equilibrium, the effector ceases to generate a response

  ◾If levels go too far in the opposite direction, antagonistic pathways will be activated to restore the internal balance
• 6.5.10 Explain the control of body temperature, including the transfer of heat in blood, and the roles of the hypothalamus, sweat glands, skin arterioles and shivering

  Temperature regulated by negative feedback;

  thermoreceptors detect temperature change;

  thermoregulatory centre (hypothalamus) in brain;

  warming the body actions:

  shivering to produce waste heat;

  no release of sweat; behaviours including increased motion / huddling / reduction of exposed surfaces;

  vasoconstriction of skin arterioles;

  leading to retention of heat;

  cooling the body actions:

  vasodilation of skin arterioles;

  leading to loss of heat by radiation;

  sweating accompanied by evaporative cooling;

  reduction of activity / relaxation of muscles;

  loss of heat by radiation;
• 6.5.11 Explain the control of blood glucose concentration, including the roles of glucagon, insulin and the alpha and beta cells in the pancreatic islets

  homeostasis is maintaining internal environment at

  constant levels / within narrow limits;

  homeostasis involves both nervous and endocrine systems;

  low blood glucose triggers glucagon release;

  glucagon is produced by α-islet cells in pancreas;

  glycogen is converted to glucose;

  high blood glucose concentration triggers insulin release;

  insulin produced by β-islet cells in pancreas;

  glucose taken up by (liver / muscle) cells;

  glucose converted to glycogen;

  blood glucose levels controlled by negative feedback;

  correct reference to lowering or raising blood glucose levels;
• 6.5.12 Distinguish between type I and type II diabetes

  
• 6.6.2 Outline the role of hormones in the menstrual cycle, including FSH (follicle stimulating hormone), LH (luteinising hormone), estrogen and progesterone

  
• 6.6.3 Annotate a graph showing hormone levels in the menstrual cycle, illustrating the relationship between changes in hormone levels and ovulation, menstruation and the thickening of the endometrium

  Follicular Phase:

  ◾FSH stimulates growth of several follicles

  ◾Dominant follicle secretes estrogen

  ◾Estrogen inhibits growth of other follicles (and FSH)

  ◾Estrogen stimulates development of endometrium

  Ovulation:

  ◾A surge in LH causes ovulation (egg release)

  ◾Rupturing of follicle creates a corpus luteum

  Luteal Phase:

  ◾Corpus luteum secretes progesterone (and estrogen)

  ◾Progesterone stimulates development of endometrium

  ◾Estrogen and progesterone inhibit FSH and LH

  ◾Corpus luteum degrades over time

  ◾When corpus luteum degrades, progesterone levels drop

  ◾Without progesterone, endometrium cannot be maintained

  ◾Endometrium is sloughed away (menstruation)

  ◾No longer inhibited, FSH can start menstrual cycle again

  ◾If fertilisation of egg occurs, the zygote releases a hormone (hCG) which maintains the corpus luteum

  
• 6.6.4 List three roles of testosterone in males

  ◾Pre-natal development of male genitalia

  ◾Development of secondary sex characteristics

  ◾Maintenance of sex drive (libido)
• 6.6.5 Outline the process of in vitro fertilisation

  (IVF) is fertilization outside body / "in glass";

  (drug) stops normal menstrual cycle;

  (inject FSH) to stimulate ovaries / stimulate production of eggs;

  (HCG) matures the follicles;

  eggs are removed from follicles / ovaries / mother;

  male provides sperm / sperm donor;

  washing / capacitation of sperm;

  eggs are mixed with sperm;

  2-3 embryos are implanted into uterus;

  pregnancy test is done to see if implantation / pregnancy has occurred;
• 6.6.6 Discuss the ethical issues associated with IVF

  Arguments against (IVF):

  fertilized egg has potential to become a person;

  IVF requires the production of multiple embryos;

  fate of extra embryos is ethical concern;

  ethics of long-term storage;

  stem-cell research is blurring issue as other cells now have the

  possibility of becoming a person;

  procedure may result in multi-embryo pregnancy which places stress on the family resources / unwanted children;

  issues of equity of access / expensive;

  high rates of failure;

  ownership for stored embryos an issue;

  religious opposition / playing God;

  Arguments favouring (IVF):

  only way some couples can have children / helps infertile couples;

  allows for genetic screening;

  allows for surrogate mothers;